Method of producing a panel and a core therefor

ABSTRACT

A method of producing a panel includes:
         placing an assembly including core elements and impregnatable material webs extending along and between the core elements on a mould, which assembly includes a first side and a second side which is situated opposite the first side,   enclosing the assembly under a cover layer in a sealing manner with respect to the mould,   introducing at least one inlet for injection material, which inlet ends at a first side of the assembly,   connecting the space which is enclosed by the cover layer and the mould to a discharge,   injecting injection material via the inlet on the first side of the assembly and causing the injection material to move along via paths formed by the material webs between the core elements,   discharging air and/or gas from the enclosed space via the discharge via underpressure at a position which is at a different level to the position where the inlet ends.

The invention relates to the production of panels, in particularsandwich panels, from fibre-reinforced plastic materials. In thisconnection, consideration may in particular be given to panels which aresubject to high loads, for example for bridge decks, which have to beable to withstand the total load which is the sum of the weight of thebridge itself and the weight of the road traffic, as well as the localloads which are caused by wheels and the like.

With the traditional process of producing such a panel, a shell is firstproduced in a mould which has the desired complementary shape of, forexample, the bridge deck. This shell consists of fibre-reinforcedplastic, as can be produced by impregnating fibre webs or mats withresin. A core is arranged on this shell, following which a second shellis then constructed. After these components have been assembledcorrectly, the semifinished product obtained is ready for furtherprocessing.

One of the drawbacks of this method is its complexity. The process inquestion comprises four steps, i.e. producing the first shell, producingthe core, placing the core on the first shell, producing the secondshell and placing the second shell on the core. This is the reason whysuch a process is time consuming. A further drawback of this method isthe risk that the interface between the core and the skins is notcompletely moistened during adhesive bonding, which may result ininclusions of air which are disadvantageous for the strength andstiffness of the resultant product.

It is therefore the object of the invention to provide a more efficientand more reliable method of producing a fibre-reinforced panel. Thisobject is achieved by means of the following steps:

-   -   placing an assembly comprising core elements and impregnatable        material webs extending along and between the core elements on a        mould, which assembly comprises a first side and a second side        which is situated opposite the first side,    -   enclosing said assembly under a cover layer in a sealing manner        with respect to the mould,    -   introducing at least one inlet for injection material, which        inlet ends at the first side of the assembly,    -   connecting the space which is enclosed by the cover layer and        the mould to a discharge,    -   injecting injection material via the inlet on the underside of        the assembly and causing the injection material to move along        via the paths formed by the material webs between the core        elements,    -   discharging air and/or gas from the enclosed space via the        discharge by means of underpressure at a position which is at a        different level to the position where the inlet ends.

With the method according to the invention, impregnating the variousparts of the panel is concentrated in one and the same production stage.In this case, the two shells and the core are simultaneously formed andattached to one another. If, in addition, the injection material issupplied directly at the underside of the panel, there is hardly anyrisk of inclusions of air forming. The front of the injection materialgradually moves upwards and during this process forces any inclusions ofair and possible other gases upwards and pushes them ahead of it, as aresult of which these can be extracted in a reliable manner. However, itis not necessary to supply the injection material to the underside.Alternatively, the material can also be supplied to the upper side sothat it gradually moves down. In this case, there may be some inclusionsof air, but this does not have to be a problem with all applications.

Preferably, prismatic cores, in particular block-like cores, are used.The material webs may extend across in each case the upper side of anumber of cores, between in each case two adjacent cores and across oralong the underside of a number of cores. In this manner, a panel isobtained which has excellent properties with regard to the totalstrength and stiffness as well as regarding the resistance against localloads. In particular, the method according to the invention may comprisethe steps of:

-   -   arranging prismatic cores parallel to one another,    -   providing injection lines which extend across the mould and on        the first side of the series and which are oriented transversely        to the core elements, which injection lines are connected to an        inlet.

The fact that the injection lines extend transversely with respect tothe core elements has the advantageous result that the injectionmaterial can be distributed evenly in the width direction across theadjacent core elements. This is a first measure which is intended tocause the front of injection material to gradually move upwards anddownwards, respectively, in an evenly distributed manner. However, partsof the material webs may be present between the various core elements.In order to be able to distribute the injection material evenly acrossthe width of the adjacent cores even in those cases, the methodaccording to the invention preferably also comprises the followingsteps:

-   -   providing in each case a passage in the material web parts which        extend between adjacent blocks,    -   providing in each case an injection line through a series of        aligned passages in the material web parts.

This means that during the construction of the core, a hole is made inthe respective part of the material webs each time a core element with amaterial web thereon is placed. To this end, it is necessary to assemblethe injection lines from parts which can each be inserted through therespective hole. According to the invention, this is achieved by thefollowing steps:

-   -   providing injection line pieces having a length dimension which        is equal to the thickness dimension of a core element,    -   inserting an injection line piece into the passage in said        material web after a core element has been placed and an        associated material web has been arranged over said core element        and attaching said injection line piece to a previously placed        injection line piece or to an inlet piece.

It is also important that the displaced air or gases can be dischargedin a regular manner, so that no local pressure differences can becreated which could disturb the formation of an evenly advancing front.To this end, the method also comprises the following steps:

-   -   placing in each case a discharge line transversely across the        second side of the core elements and across the material web        parts which extend along the core elements,    -   offsetting a discharge line in the centre between in each case        two injection lines.

The transversely placed discharge line or discharge lines ensure that,viewed in the width direction of the cores, a regular and even dischargeof the displaced air and/or gases is ensured. The offset position of thedischarge lines with respect to the inlet lines which are situated belowor above ensures that the path along which the air or the gases aredischarged is more or less the same for all cores, viewed from the inletlines. This prevents the occurrence of short-circuit flows which couldresult in the formation of an irregular front.

As has already been stressed above, it is very important that theinjection material rises again between the cores in a more even manner.In this connection, several more additional measures may be taken whichcan ensure the formation of an even front and a smooth through-flow. Byway of a first option, the following steps are mentioned:

-   -   providing core elements having in each case a groove which        extends transversely to the injection line in the first surface        thereof and side wall grooves provided in the side walls        extending parallel to said groove, which groove in the first        surface and which side wall grooves are all separated from one        another,    -   causing the injection material to flow laterally from the groove        situated in the bottom surface groove via the material of the        material webs as far as into the side wall grooves. With such        core elements, the injection material initially flows through        the groove in the first surface, that is to say usually in the        length direction of each core. As soon as such a groove is        completely filled, the injection material can only flow further        by leaving the groove. At this stage, the injection material        touches the material of the material webs, which results in a        throttling effect, thus ensuring that said material of the        material webs is moistened along the entire length of the        groove. The injection material then passes into the side wall        grooves via the material webs, as a result of which the actual        formation of the front in the upward and/or downward direction        is stimulated.

The cores may also play an important part in extracting the gases or theair. This may be achieved by the following steps:

-   -   providing core elements, each of which has groove parts which        are in the second surface thereof, are separated from one        another and end at opposite transverse sides of the cores, and        which groove parts are parallel to the side walls in which the        side wall grooves are situated, which groove parts and which        side wall grooves are all separated from one another,    -   causing the injection material to flow from the side wall        grooves as far as into the groove parts via the material of the        material webs,    -   positioning in each case a discharge line between the ends of        the groove parts facing one another in the second surface of the        core elements.

The discharge of the injection material from the side wall grooves toand into the groove parts in the second surface of the core elementsagain takes place via the material of the material web parts. In thiscase, an even distribution of the injection material is achieved againas well. The grooves in the second surface of the core elements do notextend as far as the discharge line, so that the injection materialagain first has to flow through the material of the material web partson top of the core elements before reaching the discharge line.

With relatively large structures, as will usually be the case withbridges, the problem may occur that the injection material penetratesless well along the edges of the assembly. This may be prevented by thefollowing steps:

-   -   placing at least one auxiliary injection line at least one of        the edges of the assembly,    -   in a first phase, injecting the injection material only through        those injection lines which extend transversely,    -   in a second phase, also injecting injection material through the        auxiliary injection line.

In this connection, a further improvement of the injection of theinjection material can be obtained by the following steps:

-   -   placing an annular auxiliary injection line around the assembly,    -   providing a discharge which is situated in the centre with        respect to the annular line,    -   connecting an auxiliary extraction line on one side of the        assembly in a position above the inlet line for supplying        injection material to the assembly,    -   said extraction line is connected to the inlet line by means of        a low-permeability restrictor having a low flow resistance for        gases and a high resistance for transportation of liquids,    -   extracting a portion and only a portion of the injection        material from the extraction line on the injection line, at a        location thereof situated opposite the side where the inlet is        situated,    -   extracting gases and/or air via the discharge there.

Extracting the injection material from the auxiliary extraction line hasthe advantage that the permeation of gases in the assembly on said sideis kept in check. In practice, it has been found that on that side lyingopposite the side where the inlet is situated, preferentialtransportation of gas may occur via a short-circuit flow to the centreof the assembly, in which centre the main discharge is situated. By nowextracting the injection material to a limited degree at the injectionlines on said opposite side, and thus collecting the gas before itenters the assembly, the occurrence of inclusions of air is preventedand it is still possible to achieve a high-quality impregnation.

The invention also relates to a core element for use with the method asdescribed above. This core element is in the shape of a block having afirst surface, a second surface situated opposite the first surface andmutually facing longitudinal side faces and mutually facing transverseside faces, wherein the first surface is provided with a continuousgroove which extends parallel to the longitudinal side faces.

The longitudinal side faces may furthermore be provided with continuousgrooves which extend between the first surface and the second surfaceand are separated from the groove in the first surface. The secondsurface may also be provided with two mutually separated groove parts,each of which ends at a transverse side face, which groove parts areseparated from the grooves in the longitudinal side faces. In a furtherembodiment, the first surface may be provided with opposite recesses,each of which is adjacent to a transverse side face and in which thegroove situated in said first surface ends. The injection lines may beaccommodated in said recesses.

The invention will now be explained in more detail with reference to anexemplary embodiment illustrated in the figures, in which:

FIG. 1 shows a view in perspective and in cross section of a mould withan assembly according to the invention;

FIG. 2 shows the cross section along II-II from FIG. 1;

FIG. 3 shows a perspective view of a portion of the core with lines;

FIG. 4 shows a portion of a side view of the core with lines;

FIG. 5 shows a perspective view of a core element;

FIG. 6 shows a perspective view of a core element, pipe piece andmaterial web;

FIG. 7 shows the view according to VII from FIG. 6;

FIG. 8 shows a variant of the mould with the assembly according to theinvention;

FIG. 1 shows a mould 1 on which an assembly 3 consisting of adjacentcore elements 4 and material webs 5 is arranged. This assembly 3 iscovered by the cover layer 10 which is closed along the longitudinaledges with respect to the mould 1. The mould 1 is also provided withlongitudinal elements 2 in order to give the assembly 3 a desired shapefor the production of a bridge element. In the view of FIGS. 6 and 7, itcan be seen that the material web 5 is arranged over each core element 4substantially according to a Z-shaped configuration with a material webpart 6 which covers the upper side of the respective core element 4 anda material web part 7 which covers a vertical side of the core element 4and a horizontal material web part which extends over the mould and isturned away from the core element 4. The various horizontal material webparts 6 of neighbouring material webs 5 overlap one another, as do thehorizontal material web parts 8 thereof, as can be seen in FIG. 7. Thematerial web parts 7, which extend between in each case two adjacentcore elements 4, form paths 9 via which injection material can rise, aswill be explained below in more detail.

The inlet hoses 11 extend through in each case one or more of the coreelements 4. To this end, a space may be left between two core elements4, as is shown in FIG. 2, but it is also possible to interrupt one ofthe core elements 4 in order to make space for the inlet hoses 11. Eachinlet hose 11 is connected to a transverse line 12 in such a mannerthat, as is illustrated in FIG. 2, injection material can spreadtransversely below the assembly. The transverse lines 12 are porous, insuch a manner that the injection material can gradually flow out ofthem. The view from FIGS. 3 and 4 shows that the transverse lines 12 aresituated in corresponding transverse recesses 13 of core elements 4which adjoin one another in the length direction.

To each transverse recess 13, a longitudinal recess 15 which is providedcentrally in the bottom surface of each core element 14 is connected, asis also illustrated in FIG. 5. Via this longitudinal recess 1, theinjection material initially flows over the mould 1 and the material webparts 8 situated thereon. As is illustrated in FIG. 5, said longitudinalrecess 15 extends between both opposite transverse recesses 13 of eachcore element 4. However, if the longitudinal recess is completely filledwith injection material, the latter is forced to flow out of thislongitudinal recess 15 in the transverse direction. The injectionmaterial is then pressed through the various layers composed of materialweb parts 8, resulting in a throttling effect which ensures an evendistribution of the injection material across the longitudinal dimensionof the core element 4. The injection material then flows upwards in thepaths 9 formed between adjacent core elements 4 via the material webparts 8 and the adjoining vertical material web parts 7. The verticallyextending side faces of the core elements have vertical ducts 16, 4which force the injection material to flow upwards, each path 9gradually being completely filled with injection material in theprocess. As soon as the injection material arrives at the upper surfaceof each core element 4, it is forced to flow through the horizontalmaterial web parts 6 there. In this case as well, a throttling effectoccurs, resulting in a regular distribution of the upflowing injectionmaterial across this upper surface of each core element 4. This uppersurface has two duct parts 17, 18 extending in the length direction andseparated by a wall 19. The injection material flowing across the uppersurface passes into said duct parts 17, 18 and flows to the bridge 19.

As is illustrated in FIGS. 3 and 4, a discharge line 20 extends at thelocation of the bridge 19 of the adjacent core elements 4 which are nextto one another. Via this extraction line, gases and/or air areextracted. The position of these discharge lines is chosen such thattheir path and length which the injection material has to travel fromthe transverse line 12 to the discharge line 20 is of equal length inall parts of the core. This assists in filling the core completely andwithout inclusions of air.

Reference is made to FIGS. 6 and 7 with regard to the fitting of thetransverse line 12. This inlet line 12 is composed of inlet pieces 21,the length of which is equal to the thickness of a core element 4. Assoon as a core element 4 with a material web 5 thereon has been placed,an opening 22 is made in the vertical part 7 of the material web 5, sothat an inlet line piece 21 can be inserted into said opening 22 and canbe attached to a preceding inlet piece 21. Thus, by placing the coreelements 4 and the material webs 5, the transverse line 12 is graduallyconstructed.

The variant from FIG. 8 shows that in addition to the inlet line 11 andtransverse line 12, an additional inlet line 23 and discharge line 24may be provided in the edge region of the assembly. Thus, it is ensuredthat the material webs can also be readily impregnated in those edgeregions.

Although an embodiment is described above in which the liquid issupplied from below, it is also conceivable to use the reverseembodiment in which the liquid is supplied from above.

LIST OF REFERENCE NUMERALS

-   -   1. Mould    -   2. Mould portion    -   3. Assembly    -   4. Core element    -   5. Web material    -   6. Horizontal web portion    -   7. Vertical web portion    -   8. Horizontal web portion    -   9. Path    -   10. Cover layer    -   11. Inlet line    -   12. Transverse line    -   13. Transverse recesses    -   15. Longitudinal groove in the underside of the core element    -   16. Vertical side wall groove in the side wall of the core        element    -   17. Groove portion in the upper side of the core element    -   18. Groove portion in the upper side of the core element    -   19. Wall between groove portions    -   20. Discharge line    -   21. Inlet line piece    -   22. Opening in vertical web portion    -   23. Auxiliary inlet line    -   24. Auxiliary discharge line

1. Method of producing a panel, comprising the following steps: placingan assembly (3) comprising core elements (4) and impregnatable materialwebs (5) extending along and between the core elements on a mould (1),which assembly (3) comprises a first side and a second side which issituated opposite the first side, enclosing said assembly (3) under acover layer (10) in a sealing manner with respect to the mould (1),introducing at least one inlet (11) for injection material, which inletends at a first side of the assembly (3), connecting the space which isenclosed by the cover layer (10) and the mould to a discharge (20),injecting injection material via the inlet (11) on said first side ofthe assembly (3) and causing the injection material to move along viathe paths (9) formed by the material webs (5) between the core elements(4), discharging air and/or gas from the enclosed space via thedischarge by means of underpressure at a position which is at adifferent level to the position where the inlet (11) ends.
 2. Methodaccording to claim 1, comprising the following steps: forming a seriesof prismatic, for example block-like, core elements (4), causing thematerial webs (5) to extend across in each case the upper side of theseries, between in each case two adjacent core elements (4) and acrossthe underside of the series.
 3. Method according to claim 2, comprisingthe following steps: arranging a series of prismatic core elements (4)parallel to one another, providing injection lines (12) which extendacross the mould (1) and on the first side of the series and which areoriented transversely to the core elements (4), which injection lines(12) are connected to an inlet (11).
 4. Method according to claim 3,comprising the following steps: providing in each case a passage (22) inthe material web parts (7) which extend between adjacent core elements(4), providing in each case an injection line (12) through a series ofaligned passages (22) in the material web parts (7).
 5. Method accordingto claim 4, comprising the following steps: providing injection linepieces (21) having a length dimension which is equal to the thicknessdimension of a core element (4), inserting an injection line piece (21)into the passage (22) in said material web (5) after a core element (4)has been placed and an associated material web (5) has been arrangedover said core element and attaching said injection line piece to apreviously placed injection line piece or to an inlet piece.
 6. Methodaccording to claim 5, comprising the following steps: placing in eachcase a discharge line (20) transversely across the second side of theseries of core elements (4) and across the material web parts (6) whichextend across the series, offsetting a discharge line (20) in the centrebetween in each case two injection lines (12).
 7. Method according toclaim 6, comprising the following steps: providing core elements (4)having in each case a groove (15) which extends transversely to theinjection line (12) in the first surface thereof and side wall grooves(16) provided in the side walls extending parallel to said groove, whichgrooves are all separated from one another, causing the injectionmaterial to flow laterally from the groove (15) situated in the firstsurface via the material of the material webs (5) as far as into theside wall grooves (16).
 8. Method according to claim 6, comprising thefollowing steps: providing core elements (4), each of which has grooveparts (17, 18) which are in the second surface thereof, are separatedfrom one another and end at opposite transverse sides of the coreelements (4), and which groove parts are parallel to the side walls inwhich the side wall grooves (16) are situated, which grooves are allseparated from one another, causing the injection material to flow fromthe side wall grooves (16) as far as into the groove parts (17, 18) viathe material of the material webs (5), positioning in each case adischarge line (20) between the ends of the groove parts (17, 18) facingone another in the second surface of the core elements (4).
 9. Methodaccording to claim 6, comprising the following steps: placing at leastone auxiliary injection line (23) at least one of the edges of theassembly (3), in a first phase, injecting the injection material onlythrough those injection lines (12) which extend transversely, in asecond phase, also injecting injection material through the auxiliaryinjection line (23).
 10. Method according to claim 9, comprising thefollowing steps: placing an annular auxiliary injection line (25) aroundthe assembly (3), providing a discharge (28) which is situated in thecentre with respect to the auxiliary injection line (25), supplyinginjection material to the auxiliary injection line (25) on one side ofthe assembly (3), extracting a portion and only a portion of theinjection material from the auxiliary injection line (25) at a location(27) thereof situated opposite the side where the inlet is situated,discharging gases and/or air via the central discharge (28).
 11. Coreelement (4) for use with the method according to claim 8, provided inthe shape of a block having a first surface, a second surface situatedopposite the first surface and mutually facing longitudinal side facesand mutually facing transverse side faces, wherein the first surface isprovided with a continuous groove (15) which extends parallel to thelongitudinal side faces.
 12. Core element (4) according to claim 11,wherein the longitudinal side faces are provided with continuous sidewall grooves (16) which extend between the first surface and the secondsurface and are separated from the groove (15) in the first surface. 13.Core element (4) according to claim 11, wherein the second surface isprovided with two mutually separated groove parts (17, 18), each ofwhich ends at a transverse side face, which groove parts are separatedfrom the side wall grooves (16) in the longitudinal side faces.
 14. Coreelement (4) according to claim 11, wherein the first surface is providedwith opposite recesses (13), each of which is adjacent to a transverseside face and in which the groove (15) situated in said first surfaceends.
 15. Method according to claim 1, comprising the following steps:arranging a series of prismatic core elements (4) parallel to oneanother, providing injection lines (12) which extend across the mould(1) and on the first side of the series and which are orientedtransversely to the core elements (4), which injection lines (12) areconnected to an inlet (11).
 16. Method according to claim 7, comprisingthe following steps: providing core elements (4), each of which hasgroove parts (17, 18) which are in the second surface thereof, areseparated from one another and end at opposite transverse sides of thecore elements (4), and which groove parts are parallel to the side wallsin which the side wall grooves (16) are situated, which grooves are allseparated from one another, causing the injection material to flow fromthe side wall grooves (16) as far as into the groove parts (17, 18) viathe material of the material webs (5), positioning in each case adischarge line (20) between the ends of the groove parts (17, 18) facingone another in the second surface of the core elements (4).
 17. Coreelement (4) according to claim 12, wherein the second surface isprovided with two mutually separated groove parts (17, 18), each ofwhich ends at a transverse side face, which groove parts are separatedfrom the side wall grooves (16) in the longitudinal side faces.